I used Couchsurfing when travelling around Equatorial Guinea in 2015 while researching the Bradt Guide to Equatorial Guinea: https://www.bradtguides.com/shop/equatorial-guinea.html. It was amazing, got to stay with some really cool Spanish, Colombian and Equatoguinean people all across the country.

Equatorial Guinea is quite an expensive destination so I'm not surprised that Ruta47's quote was high. A few others you might try include:

https://twitter.com/punto_grupo

https://twitter.com/gapega_ who runs https://twitter.com/guineaturismo

https://twitter.com/eurekeando

https://twitter.com/EgIsaw

https://twitter.com/RumboMalabo

P.S. I also stayed at the Seafarer's Missions in Douala and it was awesome!